1. Technical Field
The present disclosure relates to a method for the selective oxidation of alcohols into their corresponding carbonyl compounds using Ag3PO4 as a photocatalyst to oxidize at least 90% of the alcohols into their corresponding carbonyl compounds.
2. Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Selective, efficient and complete oxidation of alcohols into corresponding carbonyl compounds, such as aldehydes, ketones etc., is of paramount significance for chemical industries because carbonyl compounds are used in food, beverage, and pharmaceutical industries as well as a raw material in chemical industries (Miyamura, H.; Matsubara, R.; Miyazaki, Y.; Kobayashi, S. Angew. Chem. 2007, 119, 4229; Hundlucky, M. Oxidations in Organic Chemistry, American Chemical Society, Washington, D.C., 1990—each incorporated herein by reference in its entirety). To achieve the afore-mentioned conversions, the use of stoichiometric inorganic reagents, such as KMnO4, K2CrO4 etc., is predominantly used in these industries. Although such reagents offer high activity and selectivity, accumulation of waste products arising from the use of these inorganic reagents poses a threat to the environment. Intensive effort has been carried out in past years to develop ‘green oxidation processes’. Although there are active heterogeneous metal catalysts being developed for the aerobic oxidation of various alcohols, the reactions are carried out in harmful organic solvents and/or under vigorous conditions (Kwon, M. S.; Kim, N.; Park, C. M.; Lee, J. S.; Kang, K. Y.; Park, J. Org. Lett. 2005, 7, 1077; Enache, D. I.; Edwards, J. K.; Landon, P.; Solsona-Espriu, B.; Carley, A. F.; Herzing, A. A.; Watanabe, M.; Kiely, C. J.; Knight, D. W.; Hutchings, G. J. Science 2006, 311, 362; Yamada, Y. M. A.; Arakawa, T.; Hocke, H.; Uozumi, Y. Angew. Chem. 2007, 119, 718—each incorporated herein by reference in its entirety).
Since the discovery of water splitting on TiO2 electrode in 1970 under light (Fujishima, A.; Honda, K. Nature 1972, 238, 37—incorporated herein by reference in its entirety), the photocatalytic process has been widely investigated owing to its renewable attributes. Most of the earlier studies involving photocatalysis focused on environmental cleanup, H2 production, CO2 reduction etc. (Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W. Chem. Rev. 1995, 95, 69; Maeda, K.; Teramura, K.; Lu, D.; Takata, T.; Saito, N.; Inoue, Y.; Domen, K. Nature 2006, 440, 295; Varghese, O. K.; Paulose, M.; LaTempa, T. J.; Grimes, C. A. Nano Lett. 2009, 9, 731—each incorporated herein by reference in its entirety). Recently, utilization of the photocatalytic process for the synthesis of fine chemicals in an environmentally friendly fashion is desirable (Yoon, T. P.; Ischay, M. A.; Du, J. Nature Chemistry 2010, 2, 527; Palmisano, G.; Augugliaro, V.; Pagliaro, M.; Palmisano, L. Chem. Commun. 2007, 3425—each incorporated herein by reference in its entirety). Attempts have been made to achieve various functional group transformations such as amine to imine (Lang, X. J.; Ji, H. W.; Chen, C. C.; Ma W. H.; Zhao, J. C. Angew. Chem. Int. Ed. 2011, 50, 3934; Su, F. Z.; Mathew, S. C.; Mohlmann, L.; Antonietti, M.; Wang, X. C.; Blechert, S. Angew. Chem. Int. Ed. 2011, 50, 657; Wang, C.; Xie, Z. G.; deKrafft, K. E.; Lin, W. B. J. Am. Chem. Soc. 2011, 133, 13445—each incorporated herein by reference in its entirety), nitro to azo (Zhu, H.; Ke, X.; Yang, X.; Sarina, S.; Liu, H. Angew. Chem. Int. Ed. 2010, 49, 9657—incorporated herein by reference in its entirety), aniline to azobenzene conversion (Li, S.; Diebold, U. J. Am. Chem. Soc. 2010, 132, 64—incorporated herein by reference in its entirety), hexane to hexanone and hexanol (Ide, Y.; Kawamoto, N.; Bando, Y.; Hattori, H.; Sadakane, M.; Sano, T. Chem. Commun. 2013, 49, 3652—incorporated herein by reference in its entirety), alcohols to their corresponding aldehydes (Yurdakal, S.; Palmisano, G.; Loddo, V.; Augugliaro, V.; Palmisano, L. J. Am. Chem. Soc. 2008, 130, 1568; Maldotti, A.; Molinari, A.; Amadelli, R. Chem. Rev. 2002, 102, 3811; Palmisano, G.; Garcia-Lopez, E.; Marci, G.; Loddo, V.; Yurdakal, S.; Augugliaro, V.; Palmisano, L. Chem. Commun. 2010, 46, 7074; Augugliaro, V.; Caronna, T.; Loddo, V.; Marc, G.; Palmisano, G.; Palmisano, L.; Yurdakal, S. Chem Eur. J. 2008, 14, 4640; Wang, Q.; Zhang, M.; Chen, C.; Ma, W.; Zhao, J. Angew. Chem. Int. Ed. 2010, 49, 7976; Palmisano, G.; Yurdakal, S.; Augugliaro, V.; Loddo, V.; Palmisano, L. Adv. Synth. Catal. 2007, 349, 964—each incorporated herein by reference in its entirety), and so on. Selective oxidation of alcohols into corresponding aldehydes is one of the indispensable transformations in organic synthesis because aldehydes are being used in food, beverage, and drug industries as well as raw materials in chemical industries. Examples of the photocatalysts that are studied for alcohol oxidation include CdS/graphene (Zhang, N.; Zhang, Y.; Pan, X.; Fu, X.; Liu, S.; Xu, Y-J. J. Phys. Chem. C 2011, 115, 23501—incorporated herein by reference in its entirety), CdS/graphene (Zhang, N.; Zhang, Y.; Pan, X.; Yang, M.-Q.; Xu, Y.-J. J. Phys. Chem. C 2012, 116, 18023—incorporated herein by reference in its entirety), and Au/CeO2 (Tanaka, A.; Hashimoto, K.; Kominami, H. Chem. Commun. 2011, 47, 10446; Tanaka, A.; Hashimoto, K.; Kominami, H. J. Am. Chem. Soc. 2012, 134, 14526—each incorporated herein by reference in its entirety).
Xu et. al., studied the conversion of benzyl alcohol into benzaldehyde in the presence of CdS assembled on two-dimensional graphene scaffold under visible light in organic solvent (namely benzotrifluoride). Although the selectivity was ˜80%, the conversion and the yield were <50%. Furthermore, Xu et. al., synthesized a ternary photocatalyst involving CdS/graphene/TiO2 for the oxidation of benzyl alcohol to benzaldehyde and demonstrated that the ternary had better photocatalytic activity as compared to binary CdS/graphene. The conversion of benzyl alcohol was ˜80% while selectivity towards benzaldehyde and yield of benzaldehyde were ˜80% and <80% respectively, but the reaction was carried out in the organic solvent benzotrifluoride.
Kominami et. al. deposited Au nanoparticles on a CeO2 photocatalyst surface and studied photocatalytic chemoselective oxidation of alcohols to their corresponding aldehydes caused by plasmonic effect of Au under irradiation by green light. Although high selectivity (>99%) and a complete (>99%) oxidation of benzyl alcohol to benzaldehyde was obtained, the rate of reaction or benzaldehyde formation was extremely low (3.0 μmolh−1). In addition, disparate forms of TiO2, namely rutile,1 anatase, and brookite (Addamo, M.; Augugliaro, V.; Bellardita, M.; Paola, A. D.; Loddo, V.; Palmisano, G.; Palmisano, L.; Yurdakal, S. Catal. Lett. 2008, 126, 58—incorporated herein by reference in its entirety), and surface modified TiO2, such as Nb2O5/TiO2 (Furukawa, S.; Shishido, T.; Teramura, K.; Tanaka, T. ACS Catal., 2012, 2, 175—incorporated herein by reference in its entirety), and Pt/TiO2 (Zhai, W.; Xue, S.; Zhu, A.; Luo, Y.; Tian, Y. ChemCatChem. 2011, 3, 127—incorporated herein by reference in its entirety), have been investigated and it has been found that the rutile form is the most selective photocatalyst for the oxidation of the alcohol to its corresponding aldehyde.
In most of the studies, organic solvents were used to achieve high selectivity. The highest conversion and selectivity in water, which was 50% and 65% respectively, for the oxidation of alcohol to its corresponding aldehyde has been reported with rutile TiO2 under UV light irradiation at room temperature.
The development of active catalysts for selective and efficient conversion of alcohols to aldehydes in energy efficient and environmentally benign ways is highly desirable by chemical industries. The current disclosure describes the selective (>99%) and the exhaustive conversion (>90%) of benzyl alcohol and 4-methoxy benzyl alcohol to their corresponding aldehydes, namely benzaldehyde and 4-methoxybenzaldehyde respectively, with >99% yield, photocatalyzed by Ag3PO4 in water at room temperature and pressure under sunlight-type excitation. Moreover, >90% conversion of cinnamyl alcohol to cinnamaldehyde with >90% selectivity and >90% yield is also achieved in aqueous suspension of Ag3PO4 at room temperature and pressure under sunlight-type excitation.